1. Field of the Invention
The present invention relates to a light source with a WDM function applied to an optical communications device and an optical information processing device. The present invention also relates to an optical amplifier and a two-way optical transmission apparatus.
2. Description of the Related Art
An optical repeater for amplifying a signal light attenuated in a transmission line fiber is used in a long-distance fiber communications system. As an optical repeater, an optical fiber amplifier for directly amplifying a rare earth doped optical fiber as a gain media is well known.
In the optical fiber amplifier, it is necessary to lead with a signal light a pump light to a rare earth doped optical fiber for use in an optical amplifying operation by exciting a rare earth doped optical fiber. To attain this, the optical fiber amplifier should be designed to include a wavelength division multiplexer (WDM coupler) for division-multiplexing the signal light and the pump light.
That is, the conventional optical fiber amplifier includes a pump light source for outputting a pump light; a WDM coupler for division-multiplexing a pump light and a signal light and leading the resultant light to a rare earth doped optical fiber; and a rare earth doped optical fiber, that is, a gain media. A WDM coupler can be an optical fiber fused coupler and an optical filter made of a dielectric multi-layered film.
In the conventional optical fiber amplifier, the optical coupler for coupling a pump light source with an optical fiber and a WDM coupler are arranged after being inserted into the optical path from the pump light source to a rare earth doped optical fiber. Therefore, the output of the pump light source is attenuated by the optical coupler and the WDM coupler. As a result, the pump light power input to the rare earth doped optical fiber is reduced. This causes the problem that the gain of the signal light in the rare earth doped optical fiber is undesirably reduced.
The light source with WDM function and the optical amplifier according to the present invention aim at reducing the loss generated in the process from the pump light to the rare earth doped optical fiber so that the reduction of the gain of the rare earth doped optical fiber can be prevented. Another object of the present invention is to produce a small optical amplifier.
The light source with a WDM function according to the present invention includes a light source for outputting a light having the first wavelength; the first lens for converting the light having the first wavelength into a collimated beam; an optical output unit for outputting a light having the second wavelength; the second lens for converting the light having the second wavelength into a collimated beam; and an optical filter, provided between the first lens and the second lens, for passing the light having the first wavelength and reflecting the light having the second wavelength. The light having the first wavelength and the light having the second wavelength collected by the second lens are input to the optical input unit. Through the optical input unit, a light obtained by wavelength-multiplexing the light having the first wavelength and the light having the second wavelength is output.
The light having the first wavelength output from a light source is converted into a collimated beam and passes through an optical filter. Then, the light is collected by the second lens and coupled to the optical input unit. On the other hand, the light having the second wavelength output from the optical output unit is converted into a collimated beam by the second lens and reflected by the optical filter, and then collected again by the second lens and input to the optical input unit.
At this time, the focal point of the light having the first wavelength is made to match that of the light having the second wavelength by adjusting the incident angle of the light having the second wavelength to an optical filter plate so that the lights can be coupled in the optical input unit. Thus, the lights can be wavelength-multiplexed, and be externally output through the optical input unit.
The optical filter includes a dielectric multi-layered film formed on a substructure passing a light. The first surface of the first lens facing the second lens and the second surface of the second lens facing the first lens are flat, and an optical filter is provided at the first surface or the second surface.
The second lens can be a grated refractive index rod lens. At least the surface of the first lens on the side of the light source is convex, and the second surface of the second lens facing the first lens is flat, and an optical filter is provided at the second surface.
The first wavelength is 1480 nm band and the second wavelength is 1550 nm band, or the first wavelength is 980 nm band and the second wavelength is 1550 nm band. Otherwise, the first wavelength is 1016 nm band and the second wavelength is 1300 nm band.
The optical amplifier according to the present invention includes the above described light source with a WDM function, and the rare earth doped optical fiber connected to the optical input unit of the apparatus. In the configuration of the optical fiber amplifier, the optical input can be designed such that the light having the first wavelength collected by the second lens can be coupled with the light having the second wavelength on the surface of the rare earth doped optical fiber.
In the above described optical amplifier, when the first wavelength of the light source with a WDM function is 1480 nm band while the second wavelength is 1550 nm band, or when the first wavelength is 980 nm band and the second wavelength is 1550 nm band, an erbium doped optical fiber can be used as the rare earth doped optical fiber. On the other hand, when the first wavelength is 1016 nm band and the second wavelength is 1300 nm band, a praseodymium doped fiber is used.
The light source with a WDM function according to the present invention can be designed using a plurality of the above described light sources with a WDM function. That is, the light source includes the first light source device for outputting a light obtained by wavelength-multiplexing the light having the first wavelength xcex1 and the light having the second wavelength xcex2; and the second light source device, whose optical output unit is connected to the optical input unit of the first light source device, for outputting a new light obtained by wavelength-mulitplexing the above described wavelength-multiplexed light with the light having the third wavelength xcex3. The wavelength-multiplexed light containing the wavelengths. A wavelength-multiplexed light having the first wavelength xcex1 and the second wavelength xcex2 and a wavelength-multiplexed light having the wavelength xcex3 are output through the optical input unit of the second light source device.
Furthermore, a two-way optical transmission apparatus can be designed by using the above described light source devices. That is, there are provided a first optical transmission/reception device including the first light source device for outputting the light having the first wavelength xcex1 and receiving the light having the second wavelength xcex2 through the optical input unit, and the first receiving optics, connected to the optical output unit of the first light source device, for receiving the light having the second wavelength xcex2 and converting the light with the second wave length xcex2 into an electric signal; and a second optical transmission/reception device which has the same configuration as the first optical transmission/reception device, but has inverted wavelengths. The both devices are connected to each other through a transmission line optical fiber.